1. Field of the Invention
The invention relates to the control unit of compressor controlling the start-up operation for refrigerating machines such as air conditioners and refrigerators.
2. Description of the Related Arts
Related Art 1.
Conventional configurations and operations of the start-up control unit for refrigerating machines disclosed in the Japanese examined patent publication No. hei6-15864 are explained using FIG. 18.
Conventional compressors incorporated in refrigerating cycle machines, because a large amount of electrical current is required to start an operation of the compressor at a low temperature, tended to fail on start-up due to an activation of "protection circuit" caused from a running of excess current. That is, for a conventional compressor at low temperature, a viscosity of lubricant inside the compressor increases such that the fluidity decreases. This results not only in viscose and frictional drags at abrasive and rotational parts of the compressor, but also allows electrical current to flow easily due to a reduced electrical resistance in the motor coil under low temperature. This being the case, once the start-up failure occurs, even after a recovery from the protection circuit and then attempted to re-start, the compressor is likely to fail again. When this is repeated several times, some of the refrigerating cycle machines may take this as malfunction which can lead to a problem of shutdown of the whole machine.
Even though it will not come to the point of shutdown of the whole machine, there are situations when the machine cannot function for some length of time that this will leads to a danger of losing credibility of the refrigerating machine itself by such forceful start-up.
FIG. 18 has taken into consideration such situations, aiming to provide a start-up control unit of refrigerating cycle machines that has a heat-up function for some period of time before re-starting the machine when the failing occurs.
As FIG. 18 shows, the parts are as follows: compressor 81; pre-heating unit 82; exterior unit 83; central control unit 84; main inverter circuit 85; converter 86; inverter 87; excess current sensor 88 that detects excess current of the compressor 81; excess current detection circuit 90; and interior unit 91.
Next, operation is explained. Upon start-up, when the excess current sensor 88 in the main inverter circuit 85 has detected excess current, the detected signal is transmitted to the central processing unit 84 via the excess current detection circuit 90. At the central processing unit 84, excess current protection circuit is activated, and this stops the start-up of the compressor 81. Simultaneously, frequency output control circuit of inverter at the central processing unit 84 activates the pre-heating unit 82 to heat up the compressor 81. Using the heat from a motor of the compressor 81, a refrigerant resting inside the lubricant is poured out by heating for about 3 minutes. The refrigerant resting inside the lubricant is a medium that was liquified inside the compressor. Under a normal condition the refrigerant is carbureted to be used by the compressor 81 during the refrigerating cycle. However, due to a decreased temperature from the stopped compressor, the carbureted refrigerant is liquified, then become mixed with the lubricant. The liquified refrigerant inside the compressor is termed "resting refrigerant". An amount of liquified resting refrigerant is called "amount of resting refrigerant". The refrigerant that is carbureted due to rise in compressor temperature is used in the refrigerating cycle. The reason for pre-heating the compressor is to carburete the resting refrigerant. After pre-heating for 3 minutes, the central processing unit 84 re-activates the compressor 81. A temperature sensor 92 can be attached to the pre-heating unit 82, and the temperature reading can be transmitted to the central processing unit 84 for control.
Related Art 2.
Operation of a control unit of the compressor in conventional air-conditioners disclosed in the Japanese unexamined utility model publication No. sho56-134561 will be explained using FIGS. 19 and 20. Conventionally, when starting the air-conditioner, foaming reaction occurs from the refrigerant being mixed with the lubricant inside the compressor. The foaming of lubricant is caused by an increase in the temperature of compressor, and the lubricant is output from the compressor during refrigerating cycle. This results in a shortage of the lubricant, which causes lots of incident of burning of abrasive parts of the compressor.
To prevent such incidents, a heater was attached to a sealed container of the compressor as shown in Related Art 1; then the compressor was heated to prevent a melting of the refrigerant into the lubricant. However, such a configuration needs a power supply for the heater. The disadvantages were wasting of power, and an addition of extra parts as heater and cables for the heater.
FIGS. 19 and 20 show a configuration of conventional air-conditioner and a block chart of the control unit in Related Art 2. The parts are: compressor 61 containing motor 66 and compressor unit 69 which are designed to be contained inside a sealed container 67. Other parts are: condenser 62; decompressor 63; and evaporator 64. The compressor 61 is connected with the other parts to form a loop to comprise a well-known refrigerating cycle. When the compressor is not rotating, the lubricant 68 resides at an inner bottom of the compressor 61, and most part of the refrigerant are melted to the lubricant. Control unit 65 controls the operation of the compressor 61 and is equipped with the followings: frequency conversion circuit 65a; frequency command circuit 65b; timer circuit 65c which controls the frequency command circuit 65b; and load detection circuit 65d which detects loads on the air-conditioner. 70 is operating switch.
The operation of air-conditioner for above-mentioned configuration is explained below.
First of all, turn on the operating switch 70, and an output command of frequency 0 c/s (cycles/second) is generated to the frequency conversion circuit 65a from the frequency command circuit 65b. The frequency output of 0 c/s from the frequency conversion circuit 65a is made, or in other words, a DC (direct current) is supplied to the motor 66 of the compressor 61. The motor 66 heats up without rotating when the DC flows through. The heat from the motor 66 will heat-up the sealed container 67 and the lubricant 68. Due to this the refrigerant that was melted into the lubricant 68 becomes carbureted and will be separated from the lubricant 68.
The timer circuit 65c is activated after a fixed time t has lapsed, and the frequency command circuit 65b will be controlled by the load detection circuit 65d. As FIG. 21 shows, when the output from the frequency command circuit 65b changes, the frequency output from the frequency conversion circuit 65a will change from 0 c/s to a certain frequency (e.g. frequency in which the motor 66 starts), then the motor 66 will starts rotation and outputs high pressure gas from the compressor 61. This being the case, the refrigerant that is melted into the lubricant 68 should be small, therefore, foaming of the lubricant 68 will not occur, and only the refrigerant gas is output from the compressor 61.
Therefore, when the operation of compressor 61 starts, the burning of each abrasive part of the compressor 61 caused by the shortage of lubricant 68 can be prevented. Also, extra electricity for heating is not necessary.
The frequency output is set to 0 c/s, however, it is also possible to apply a low frequency to cause zero or small number of rotations of the motor 66. Apart from the two types of frequency in the frequency conversion control, can also design a configuration which is controlled by a gradual increase in the frequency. In addition, a period of time for controlling the frequency command circuit 65b by the load detection circuit 65d is determined using a timer, but it can also be done by temperature reading of the compressor 61.
For the conventional operation control unit of air-conditioner, upon starting the compressor, frequency is set to either zero or to a lower frequency so that the rotation of compressor is stopped or reduced. From a heat generated from the coil of motor, the compressor is heated up to evaporate the refrigerant melted into the lubricant. The compressor is designed to rotate after the evaporation that it possesses a number of advantages as: prevention of burning of each abrasive part caused by the shortage of lubricant; and no extra parts are needed such as heater and cables for the heater.
3. Problems to be solved by the Invention
As explained above, for the start-up control unit of refrigerating machine in Related Art 1, after detecting excess current of compressor the compressor 81 is turned off for a fixed amount of time (3 minutes) for heating, and then tries to re-start. Similarly, for the operating control unit of refrigerating machine in Related Art 2, the compressor starts after heating the compressor for a fixed time t using the heat generated from the coil of motor. As can be seen in both cases of Related Arts 1 and 2, the start-ups are controlled without any bearing to the amount of resting refrigerant inside the compressors. Therefore, the problem is: it does not take into account the fact that an immediate re-starting is possible. That is, even in a situation when the resting refrigerant requires only a short heating time (i.e. case when the amount of resting refrigerant is low), and the excess current has flown, it must always stop and wait for a fixed amount of time (3 minutes or time t) before re-starting. When the amount of resting refrigerant is large, on contrary, the 3 minutes or time t may not be enough heating time but it is set to re-start in that period, resulting in consumption of extra energy, in addition, a too much rise in temperature of the motor of compressor can cause various troubles (e.g. burning of abrasive parts from rise in lubricant temperature).
Also, various incidents can result from foaming of the lubricant, making re-starting even more difficult.